package pers.mingshan.thread.thread;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
/**
 * 信号量
 * @author mingshan
 *
 */
public class SemaphoreTest {
    public static void main(String[] args) {
        ExecutorService service = Executors.newCachedThreadPool();
        final  Semaphore sp = new Semaphore(3);
        for (int i = 0; i < 10; i++) {
            Runnable runnable = new Runnable() {
                public void run() {
                    try {
                        sp.acquire();
                    } catch (InterruptedException e1) {
                        e1.printStackTrace();
                    }

                    System.out.println("线程" + Thread.currentThread().getName() +
                            "进入，当前已有" + (3-sp.availablePermits()) + "个并发");
                    try {
                        Thread.sleep((long)(Math.random()*10000));
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println("线程" + Thread.currentThread().getName() +
                            "即将离开");
                    sp.release();
                    // 下面代码有时候执行不准确，因为其没有和上面的代码合成原子单元
                    System.out.println("线程" + Thread.currentThread().getName() +
                            "已离开，当前已有" + (3-sp.availablePermits()) + "个并发");
                }
            };

            service.execute(runnable);
        }

        service.shutdown();
    }

}
